The present invention relates to industrial communication networks; and more particularly, it relates to a diagnostic test system for performing a wide range of diagnostic tests in situ on an industrial communication network using a hand-held meter of convenience size.
Industrial automation installations have used programmable logic controllers (PLCs) in combination with a variety of individual devices, such as presses, robots, visual displays, solenoid actuators and many others, for achieving efficient information communication and control in manufacturing environments. A communication network employing its own protocol and signal specifications is typically used to interface all of the various devices required to be connected together. One network protocol has grown to become the current leading device-level network standard for industrial automation. That is the DeviceNet protocol. Thus, the present invention, though not so limited, is disclosed in the context of such a network.
As with any network, there is a need to test the network during original installation and, later, during normal preventive maintenance as well as when faults occur to ensure proper operation. Some network analysis tools simply establish continuity and perform no diagnostic measurements of active devices normally operated on the system nor of the signal levels or data streams typically employed in the system. Such tools are of limited use in the complex networks of modern industrial automation systems.
Networks of this type, considering the physical connections, the nature of the various types of devices which may be employed, including PLCs and personal computers and display devices, as well as the signal protocols, can be very difficult to diagnose when a problem arises. Obviously, in the case of a system which is operating a production line, if a problem arises, there is a need to identify immediately and correct the problem. Because of the different layers of physical and electronic systems employed, the skill level of a person adequate to perform diagnostic routines at all levels has become quite high. Yet, it is not economical to have a specialized person of such a high skill level simply waiting until a fault occurs because, despite the occurrence of occasional faults, the systems are quite reliable.
It is much more economical to have the initial measuring or testing of the network conducted by maintenance personnel normally in the manufacturing area on a regular basis, such as electricians, and to provide such personnel with simple, easy-to-use and readily understandable equipment which is economical to purchase, and may be assembled rapidly to the troubled network without the need to shut the system down.
The present invention addresses the problem of providing an economical test meter having the capability of performing test and diagnostic measures on an industrial automation communication network in situ by personnel having the training at the level of an electrician or the like, rather than an electronic engineer or network specialist. Depending upon the nature of the apparent problem, the on-site personnel may then correct the problem or consult an engineer or other specialist having further expertise in the area. In addition, the present invention enables the technician or operator to store (or xe2x80x9cfreezexe2x80x9d) data recorded during his or her diagnostic test procedures on the network for subsequent use or subsequent analysis.
The invention is provided in the form of a meter in a housing sized to fit comfortably in one hand of a user, leaving the other hand free to rotate a switch to the various test positions. A connector is provided for coupling the device to the network under study. Signal lines couple the data signals as well as the bus power supply voltage (xe2x80x9cVbusxe2x80x9d) and the voltage of the shield lead (xe2x80x9cVshieldxe2x80x9d) to signal conditioning circuitry.
A display (liquid crystal display, or LCD in the illustrated embodiment) is included. The display is operated by an interface data processor coupled to the main data processor (simply xe2x80x9cprocessorxe2x80x9d) by means of a bus. Additional memory is provided for the main processor.
As used herein, a xe2x80x9cnetworkxe2x80x9d includes a series of devices, such as computers, programmable logic controllers, displays, sensors, control elements or the like, commonly used in industrial automation systems. A xe2x80x9cnodexe2x80x9d is any such device connected to the network, including, for example, the test device of the present invention. According to DeviceNet protocol (an industrial communication protocol standard based on the CAN or Controller Area Network, protocol standard), there are two data signal lines, one designated as the CAN High or xe2x80x9cCANHxe2x80x9d line and the other is designated CAN Low or xe2x80x9cCANLxe2x80x9d, according to convention. The system of the present invention employs a main processor receiving the incoming data signals and sampling those signals for an accurate determination of amplitude which is then converted to a corresponding digital signal representation and stored in memory to establish a database of recorded signal measurements for various network signal parameters, to be described. The operator uses the rotary switch to access data stored in the main processor memory and to display that data.
The present system provides a wide range of diagnostic information, disclosed in more detail within. By way of example, two switch positions (positions 10 and 11 in the illustrated embodiment) may be selected by the operator to display the CANL voltage for the recessive bit (switch position 10), and for the dominant bit (position 11) of the signal. As each measurement for a given data frame is made, the system stores a xe2x80x9clivexe2x80x9d value, a maximum value and a minimum value for both the CANH and CANL signals, for the dominant bit and the recessive bit. These values in the illustrated embodiment are not associated with a specific node, although the invention is not so limited because the data identifying the node is available to the processor, if desired. The xe2x80x9clivexe2x80x9d values are overwritten in memory so that only the most current signals are retained in memory. However, the maximum and minimum values are replaced only if the previously stored values are exceeded (in absolute value).
The main processor also computes a signal value referred to as the Relative Node Common Voltage from the recorded database and then determines the worst-case (i.e., maximum) difference between any two Relative Node Common Voltages for the system under test. This difference is defined as the network Common Mode Voltage; and it is deemed to be a significant factor in determining whether the network is acceptable, marginal or unacceptable in its operation. The network Common Mode Voltage is also displayed upon the operator""s election (switch position 5).
Switch positions display the differential instantaneous voltage between CANH and CANL. The main processor subtracts the CANL voltage from the CANH voltage, and the system displays the differential voltage for the dominant bit (rotary switch position 7) and the recessive bit (rotary switch position 6). Again, live MAX and MIN values are stored and may be displayed by the operator. The system computes and displays the Common Mode Voltage measured by the system in switch position 5.
These measurements have been found to provide substantial information to the user in isolating and diagnostic network problems. Of particular significance is the fact that the main processor stores predetermined limits for ranges of acceptance for each of the conditions being measured and divides or groups the ranges of potential measurements into xe2x80x9cacceptable,xe2x80x9d meaning that the parameter being measured and displayed is within normal operating ranges, xe2x80x9cmarginal,xe2x80x9d meaning that the particular parameter being measured and displayed is acceptable but not within the desired range, or xe2x80x9cunacceptable,xe2x80x9d meaning that the value is outside operating specifications. Each of these three conditions is indicated by actuating a graphic representation of the condition which, in the illustrated embodiment, takes the form of a xe2x80x9chappyxe2x80x9d face indicating acceptable operating conditions, a xe2x80x9cneutralxe2x80x9d face indicating marginal conditions or a xe2x80x9csadxe2x80x9d face indicating unacceptable conditions.
Other positions on the rotary switch display measurements of bus power voltage, bus data traffic, bus errors and shield voltage, as will be discussed further below.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed disclosure of the exemplary embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.